This invention relates to polypropylene formulations and particularly relates to polypropylene formulations containing hindered amine light stabilizers to which small amounts of fluoborate salts are added for improved color and water carry-over properties.
Extruded polypropylene resins used for films, fibers and molded articles generally contain primary and secondary antioxidants as well as special additives for particular end uses such as pigments, UV stabilizers, thermal stabilizers, peroxides, antistats, fillers, impact modifiers, flame retardants, and the like. Primary antioxidants include, for example, hindered phenols such as 2,6 di-t-butyl-p-cresol, octadecyl-3,5-di-t-butyl-4-hydroxyhydrocinnamate, tetrakis (methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)) methane, and tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate. These usually are incorporated in polypropylene resins at concentration levels of about 0.01 to about 0.5 wt.% and typically about 0.04 to about 0.1 wt.%.
Secondary antioxidants include the organic phosphites such as, for example, distearyl pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl)phosphite, tetrakis(2,4,-di-t-butylphenyl)-4,4'- bisphenylene diphosphonite and tris (mixed mono- and dinonylphenyl) phosphite. These act in combination with the primary antioxidant and are sometimes added to the polypropylene resin at about the same range of concentration as the primary antioxidant. The special additives vary broadly depending on the particular type of additive and the end use requirements.
Polypropylene resin compositions also usually include acid scavenger agents or acid neutralizers, such as calcium stearate, zinc stearate, calcium oxide, magnesium/aluminum hydroxycarbonate, dihydroxy talcite and calcium pelargonate, at concentrations generally of about 0.01 to about 0.1 wt.%. The purpose of these agents is to neutralize acid residues derived from the polymerization catalyst which will lower the corrosivity of the resulting polymer composition.
Such resins often additionally include hindered amine light stabilizers such as N-N'-bis(2,2,6,6-tetramethyl-4- piperidinyl)-1,6-hexanediamine, polymer with 2,4,6-trichloro-1,3,5-triazine and 2,4,4-trimethyl-1,2-pentanamine sold under the trademark Chimassorb 944FL by Ciba-Geigy, poly((6-morpholino-s-triazine-2,4-diyl)-((2,2,6,6-tetramethyl-4-piperidyl) imino)-hexamethylene ((2,2,6,6- tetramethyl-4-piperidyl)imino)) sold under the trademark Cyasorb UV3346 by American Cyanamid, and bis(2,2,6,6- tetramethyl-4-piperidinyl)sebacate sold under the trademark Tinuvin 770 by Ciba-Geigy. These are added to protect the resin from degradation due to ultraviolet light exposure from sunlight.
Incorporation of fluoborates into polymer compositions has been disclosed generally for fire retardant or mineral filler purposes. U.S. Pat. Nos. 3,730,940 and 3,730,942 disclose flame retardant compositions of polypropylene and polyethylene, respectively, containing 2-10 wt.% halogenated organic flame retardant, 5-10 wt.% ammonium fluoborate or ammonium sulfate, 5-10 wt.% metal synergist and about 15-25 wt.% silica.
U.S. Pat. No 3,635,866 discloses flame retardant polybutene-1 compositions containing 4-8 wt.% ammonium fluoborate, antimony trioxide and another halogenated compound.
U.S. Pat. No. 3,493,535 discloses a polyethylene maleate diester graft copolymer which may contain 5 to 100 parts per 100 parts of polymer of solid inert particulate material, such as ammonium fluoborate, which is rigid and does not react with the molten graft copolymer.
U.S. Pat. No. 3,785,859 discloses treating natural or synthetic fibers with an aziridinyl phosphine oxide containing a halogen and an acid curing catalyst ammonium borofluoride. Polypropylene fibers are not specifically disclosed in this patent.
U.S. Pat. No. 3,287,312 discloses a flame resistant cross-linked polyethylene composition containing 4-20 wt.% inorganic fluoborate such as ammonium fluoborate, sodium fluoborate and potassium fluoborate.
French Patent document 1,448,571 discloses a flame retardant polypropylene composition which may contain 5-75 wt.% preferably 10-50 wt.% fluoborate such as zinc fluoborate tetramine and nickel fluoborate hexamine.
USSR Patent document 1070143A discloses a low-density polyethylene composition containing 30-70 wt.% aluminum or ammonium fluoborate as a mineral filler.
None of the above-described publications describes a polypropylene composition containing a hindered amine to which small amounts of a fluoborate salt are added to act as an acid scavenger and for improvement of color and water carry-over properties.
It is well-known in the art that different additive packages are used depending on the desired properties or use of the resulting polypropylene formulation. Two properties of polypropylene compositions which may be affected by the additive package are color, expressed as the yellowness index, and water carry-over. Yellowness index is the magnitude of yellowness under daylight illumination of homogeneous, nonfluorescent, nearly colorless, transparent or nearly white translucent or opaque plastics relative to magnesium oxide. See ASTM Standards D1925-70 (1977), incorporated herein by reference. Water carry-over is an effect observed in extruding a film from a melt in which the film is cooled in a water bath. As a film moves through the water bath, water may adhere to the polymer and be carried along with the film. Water carry-over is expressed as the rate at which a film can be extruded before water is carried along with the film. The higher the water carry-over value, the faster and more economically a resin film can be processed.
In this invention, small amounts of fluoborate salts such as sodium fluoborate, potassium fluoborate, and ammonium fluoborate, when used as additives to polypropylene compositions, neutralize acidic catalyst residues as efficiently as some of the commonly used acid scavenger additives (as measured by the corrosion rating) while providing the additional benefit of better (higher) water carry-over values and lower yellowness index values. This effect is seen specifically in an additive package containing hindered amine light stabilizers. These fluoborates show definite improvement over typical acid scavengers alone such as synthetic dihydroxy talcite (DHT-4A, Kyowa Chemical), magnesium/aluminum hydroxycarbonate (L55R, Reheis Chemical) and calcium stearate.